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The four phases of oestrus in cows

Similarly to other domestic animals the oestrus cycle in the cow can be divided into four phases:

1. Proestrus
2. Oestrus
3. Metoestrus
4. Dioestrus

Also see Graph oestrus cycle and Hormonal function for more information.

Proestrus

Day 17-20

• regression of the corpus luteum of the previous cycle and drop in the progesterone concentrations in circulation.
• the dominant follicle is selected and grows producing increasing amounts of oestradiol. For more information see Follicular Development .

In late proestrus, the influence of oestrogens on the reproductive tract and behaviour of the cow can be observed.

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Pre-ovulatory follicle.

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Ovary with follicles

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Ultrasonograph of follicles on an ovary

Oestrus

Traditionally considered as day 0 of a new cycle
The dominant follicle reaches its maximum growth, matures and ovulates.
Ovulation takes place approximately 30h after the onset of oestrus and after the behavioural signs of oestrus have ceased.

Ovulation is induced by high LH concentrations (preovulatory LH peak).

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Dominant follicle

Oestrus is also called heat and lasts on average 4-24 hours. During oestrus the cow/heifer is receptive to a bull and stands for mating (standing heat).

Behavioural signs of oestrus are due to the influence of oestrogens:

• restlessness
• drop in milk production
• standing to be mounted
• presence of clear mucus
• swelling and reddening of vulva

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Click here to view images of cows in oestrus

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Metoestrus

Day 2-4

• oestrus ends
• a corpus luteum (CL) is formed
• progesterone levels in circulation begin to rise

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Corpus luteum

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Corpus luteum

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Corpus luteum (usg)

Metoestrus bleeding
During this time a phenomenon known as “metoestrus bleeding” occurs in approx. 90% of heifers and not more than 45% of cows. Patches and streaks of blood are seen in the vaginal mucus staining the tail and perineum.
Remember: the presence of blood in the mucus is not an indication of conception or a failure to conceive.

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Dioestrus

Day 5-17

• period of maximum corpus luteum size and function
• high levels of progesterone in circulation
• at the end of dioestrus, luteolysis of the corpus luteum begins. For more information see Mechanisms of luteolysis.

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